Microhyla, commonly known as the rice frogs or narrow-mouthed frogs, is a genus of frogs in the family Microhylidae. It consists of 42 species of diminutive frogs.[1] Members of this genus are widespread from Ryukyu Is. in Japan, and throughout South-east Asia, (China, Sumatra, Java, Bali, Borneo, India and Sri Lanka).[2]
In 2021, nine species of Microhyla were moved to Nanohyla on the basis of morphological and phylogenetic differences.[1] Microhyla pulverata was found to be a junior synonym of Nanohyla marmorata based on phylogenetic evidence.[3]
According to Seshadri et al. (2016),[4] this genus can be diagnosed using the following set of criteria: Adult frogs are of small size; pupil circular; skin on dorsum smooth; lateral side of body with markings from back of eye to vent; supratympanic fold present in adults; paratoid glands are absent, fingers without webbing, finger tips may or may not be dilated; oval tongue, its margin is entire and free at the base; the diameter of eye is smaller than snout; a thin layer of skin hides the tympanum; tubercles on hand distinct; distinct oval shaped inner metatarsal tubercle and rounded outer metatarsal tubercle; webbing in feet, rudimentary.
The genus Microhyla is closely related to Glyphoglossus within the family Microhylidae.[2][5] Members of the genus Microhyla began diversifying from the most common ancestor around 45 million years ago and this resulted in forming Metaphrynella and Microhyla.[5] However, ascertaining the phylogenetic relationship of frogs within Microhyla has been difficult as many species are not monophyletic.[6]
A 2021 study on the relationship between Microhyla and Glyphoglossus found that nine species within Microhyla actually belong to a separate lineage. They have been subsequently moved to the new genus, Nanohyla.[1]
The following phylogeny of the genus Microhyla is from Khatiwada, et al. (2017).[12] 27 species are listed, including various newly described species from South Asia. (Note: the chart below includes some species that have since been moved to Nanohyla including N. annectens and N. perparva.)